The present invention is directed to device and method for establishing temperature compensation factors for digital load cells. More particularly, the present invention is directed to a device and method for establishing temperature compensation factors across the full span of digital load cells during the manufacture thereof.
A digital load cell, as the term is used herein, may generally include a column or other load-bearing element designed to support a load to be weighed, one or more strain gauges associated with the load-bearing element and provided to generate a signal(s) representative of the load on the load-bearing element, an analog-to-digital (A/D) converter for converting analog output signals of the strain gauges to digital signals, and a microprocessor and associated circuitry for interacting with the A/D converter for processing and transmitting the digital signals. Such a load cell may also include memory for storing various correction coefficients, etc. A thorough description of one such embodiment of a digital load cell is presented in U.S. Pat. No. 4,815,547 to Benny N. Dillon et al. As explained therein, when the load-bearing element of such a load cell is a column, the column may be, but is not required to be, designed as a self-erecting rocker pin.
In the course of digital load cell production, it is desirable to establish a consistent output from each load cell. Determining this output requires the calculation of a number of different performance characteristics that will change from load cell to load cell based on material and manufacturing variations therebetween. Therefore, the output of such load cells must typically be altered (compensated) to account for such variations.
Digitally compensated load cells need to be thermally stabilized and tested at various temperatures in order to identify the performance characteristics and establish the appropriate compensation factors at each of those temperatures. This is typically accomplished by connecting a load cell of interest to a measurement instrument, raising the temperature of the load cell to a stable temperature, and then taking the measurement(s).
The most common method for providing the range of temperatures necessary for the aforementioned testing process involves placing a load cell of interest into a temperature compensation chamber that uses typical HVAC components to convectively generate and maintain various desired testing temperatures therein. Unfortunately, there are a number of disadvantages to the use of such a device and method. For example, known temperature compensation chambers tend to be large in size due to the fact that a chamber must house a load application device (for performing temperature compensation at points other than zero load) in addition to the load cell being tested. As a result of their large size, a significant amount of time is often required for known temperature compensation chambers to reach an initial load cell thermal stabilization temperature and/or to cycle through additionally elevated load cell thermal stabilization temperatures. As such, a considerable amount of energy is also generally required to operate such a temperature compensation chamber.
A device and method of the present invention improves the efficiency of the temperature compensation process described above. A device and method of the present invention overcomes the aforementioned drawbacks associated with known devices and methods for effecting digital load cell temperature compensation.